1. Field
The present invention relates to heat recovery steam generators. Specific embodiments relate to methods for pre-assembling, transportation and installation of modules of a heat recovery steam generator.
2. Description of the Related Art
A heat recovery steam generator or HRSG is an energy recovery heat exchanger that recovers heat from a hot gas stream. An HRSG produces steam that can be used in a process (cogeneration) or used to drive a steam turbine (combined cycle).
For example, in a combined cycle power generation, the exhaust gas from a combustion turbine becomes the heat source for the Rankine cycle portion of the combined cycle. An HRSG disposed downstream of the combustion turbine exhaust recovers the waste heat available in the combustion turbine exhaust gas. The recovered heat is used to generate steam at high pressure and high temperature, and the steam is then used to generate power in the steam turbine/generator.
The HRSG is basically a heat exchanger composed of a series of functional units, namely, economizers (preheaters), evaporators, reheaters, and superheaters. The functional units comprise heat exchanger tubes disposed in a flow path of the exhaust gas from the combustion turbine. The heat exchanger tubes carry a medium comprising water and/or steam to which heat from the exhaust gas is transferred, to produce steam at high temperature and pressure.
In a modular HRSG construction, the various functional units may be constructed as separate modules. The modules may be pre-fabricated and transported to an installation site where they are installed. In a modular HRSG construction, the on-field installation cost may be reduced by providing a higher degree of pre-fabrication. However, shipping costs associated with transportation of pre-fabricated modules increases with higher degree of pre-fabrication.
A modular HRSG construction typically results in a compromise between the on-field installation cost and shipping cost, as a result of which both of these costs cannot be simultaneously contained. For example, current approaches make it possible either to achieve a lower on-field installation cost by providing a high degree of prefabrication, but with the result of correspondingly high shipping costs, or to alternately achieve a lower shipping cost by providing a lower degree of fabrication, but with the result of high on-field installation cost.